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Abstract:

In a simplified light sensing circuit, a light sensing apparatus
including the light sensing circuit, a method of driving the light
sensing apparatus, and an image acquisition apparatus and optical touch
screen apparatus including the light sensing apparatus, the light sensing
circuit includes an oxide semiconductor transistor including a channel
layer including an oxide semiconductor material, for each pixel. The
oxide semiconductor transistor is configured to operate as a light
sensing device that senses light and a switch that outputs light sensing
data.

Claims:

1. A light sensing circuit, comprising: an oxide semiconductor transistor
including a channel layer including an oxide semiconductor material,
wherein the oxide semiconductor transistor is configured to operate as a
light sensing device that senses light and a switch that outputs light
sensing data.

2. The light sensing circuit of claim 1, further comprising: a gate line
connected to a gate of the oxide semiconductor transistor and configured
to provide a gate voltage; a drive voltage line connected to a drain of
the oxide semiconductor transistor and configured to provide a drive
voltage; and a data line connected to a source of the oxide semiconductor
transistor and configured to provide data.

3. The light sensing circuit of claim 2, further comprising: a gate
driver configured to provide the gate voltage to the gate of the oxide
semiconductor transistor via the gate line, wherein the gate driver is
configured such that the gate voltage is any one of a first voltage that
is lower than a first threshold voltage, a second voltage that is between
the first threshold voltage and a second threshold voltage, and a third
voltage that is positive, the first threshold voltage being a threshold
voltage of the oxide semiconductor transistor when light is incident on
the oxide semiconductor transistor, the second threshold voltage being a
threshold voltage of the oxide semiconductor transistor when light not
incident on the oxide semiconductor transistor.

4. The light sensing circuit of claim 1, further comprising: a gate line
connected to both of a gate and a drain of the oxide semiconductor
transistor and configured to provide a gate voltage; and a data line
connected to a source of the oxide semiconductor transistor and
configured to provide data.

5. The light sensing circuit of claim 4, further comprising: a gate
driver configured to provide the gate voltage to the gate of the oxide
semiconductor transistor via the gate line, wherein the gate driver is
configured such that the gate voltage is any one of a first voltage that
is lower than a first threshold voltage, a second voltage that is between
the first threshold voltage and a second threshold voltage, and a third
voltage that is positive, the first threshold voltage being a threshold
voltage of the oxide semiconductor transistor when light is incident on
the oxide semiconductor transistor, the second threshold voltage being a
threshold voltage of the oxide semiconductor transistor when light not
incident on the oxide semiconductor transistor.

6. The light sensing circuit of claim 1, wherein the oxide semiconductor
transistor further includes a substrate; a gate on at least a portion of
the substrate; a gate insulation film on the substrate and the gate to
cover at least the gate; a source and a drain on opposite sides of the
channel layer; and a transparent insulation layer covering the source,
the drain, and the channel layer, wherein the channel layer is on the
gate insulation film and facing the gate.

7. The light sensing circuit of claim 6, wherein the oxide semiconductor
transistor further includes a first conductive plug that passes through
the transparent insulation layer and is electrically connected to the
source; a first contact on the transparent insulation that electrically
contacts the first conductive plug; a second conductive plug that passes
through the transparent insulation layer and is electrically connected to
the drain; and a second contact on the transparent insulation layer that
electrically contacts the second conductive plug.

8. The light sensing circuit of claim 1, wherein the oxide semiconductor
transistor comprises: a substrate; a gate insulation film on at least a
central portion of the channel layer; a gate on the gate insulation film
that faces the channel layer; a source and a drain on the channel layer
at opposite sides of the gate, the source and drain each being separate
from the gate; and a transparent insulation layer covering the gate, the
source, and the drain, wherein the channel layer is on the substrate.

9. The light sensing circuit of claim 1, wherein the oxide semiconductor
material includes one or more of ZnO, InO, SnO, InZnO, ZnSnO, or InSnO,
or a material formed by adding at least one of Hf, Zr, Ti, Ta, Ga, Nb, V,
Al, and Sn to one of ZnO, InO, SnO, InZnO, ZnSnO, or InSnO.

10. A light sensing apparatus, comprising: a light sensing pixel array
including a plurality of light sensing pixels in a plurality of rows and
a plurality of columns; and a gate driver including a plurality of gate
lines in a row direction, the gate driver being configured to provide a
gate voltage and a reset signal to each of the plurality of light sensing
pixels via the plurality of gate lines, wherein each of the plurality of
light sensing pixels includes an oxide semiconductor transistor
configured to operate as a both a light sensing device that senses light
and a switch that outputs light sensing data.

11. The light sensing apparatus of claim 10, wherein the gate driver is
configured to apply the gate voltage to the oxide semiconductor
transistors sequentially in the row direction, and to apply the reset
signal to all of the oxide semiconductor transistors at a time after
applying the gate voltage to the oxide semiconductor transistors
sequentially in the row direction.

12. The light sensing apparatus of claim 10, wherein the gate driver is
configured to provide each oxide semiconductor transistor with a first
voltage that is lower than a first threshold voltage, a second voltage
that is between the first threshold voltage and a second threshold
voltage, and a third voltage that is positive, the first threshold
voltage being a threshold voltage of the oxide semiconductor transistor
when light is incident on the oxide semiconductor transistor, the second
threshold voltage being a threshold voltage of the oxide semiconductor
transistor when light not incident on the oxide semiconductor transistor.

13. The light sensing apparatus of claim 12, wherein the gate driver is
configured to provide the gate voltage to each oxide semiconductor
transistor in order of the first voltage, the second voltage, the first
voltage, and the third voltage, and the third voltage is the reset signal
to reset the oxide semiconductor transistor.

14. The light sensing apparatus of claim 10, wherein each gate line is
connected to light sensing pixels, from among the plurality of light
sensing pixels, that are in the same row.

15. The light sensing apparatus of claim 14, wherein gates of the oxide
semiconductor transistors of the plurality of light sensing pixels in a
row are connected to the gate line of the same row.

16. The light sensing apparatus of claim 10, further comprising: a signal
output unit that includes a plurality of data lines in a column
direction, the signal output unit being configured to receive a light
sensing signal from each of the plurality of light sensing pixels and
output a data signal.

17. The light sensing apparatus of claim 16, wherein sources of the oxide
semiconductor transistors of the plurality of light sensing pixels in a
column are connected to the data line of the same column.

18. The light sensing apparatus of claim 16, wherein the signal output
unit includes an A/D converter configured to convert analog signals
output from the plurality of light sensing pixels into digital signals; a
buffer configured to temporarily store the digital signals; and a column
scanner configured to select an output from one of the plurality of light
sensing pixels in a column.

19. The light sensing apparatus of claim 10, wherein the oxide
semiconductor transistor comprises: a substrate; a gate on at least a
portion of the substrate; a gate insulation film on the substrate and the
gate that covers at least the gate; a channel layer on the gate
insulation film and facing the gate; a source and a drain on opposite
sides of the channel layer, respectively; and a transparent insulation
layer covering the source, the drain, and the channel layer, wherein the
channel layer is formed of an oxide semiconductor material.

20. The light sensing apparatus of claim 19, wherein the oxide
semiconductor material includes one or more of ZnO, InO, SnO, InZnO,
ZnSnO, or InSnO, or a material formed by adding at least one of Hf, Zr,
Ti, Ta, Ga, Nb, V, Al, and Sn to one of ZnO, InO, SnO, InZnO, ZnSnO, or
InSnO.

21. The light sensing apparatus of claim 10, wherein the oxide
semiconductor transistor comprises: a substrate; a channel layer on the
substrate; a gate insulation film on at least a central portion of the
channel layer; a gate on the gate insulation film that faces the channel
layer; a source and a drain on the channel layer at opposite sides of the
gate, the source and drain each being separate from the gate; and a
transparent insulation layer covering the gate, the source, and the
drain, wherein the channel layer is formed of an oxide semiconductor
material.

22. An image acquisition apparatus, comprising: the light sensing circuit
of claim 1 in a pixel.

24. An optical touch screen apparatus, comprising: a display apparatus
configured to display an image; an optical touch panel attached on a
screen of the display apparatus, the optical touch panel including the
light sensing circuit of claim 1 in a pixel; and a light source apparatus
configured to provide an optical signal to the optical touch panel.

25. An optical touch screen apparatus, comprising: a display apparatus
configured to display an image; an optical touch panel attached on a
screen of the display apparatus, the optical touch panel including the
light sensing apparatus of claim 10; and a light source apparatus
configured to provide an optical signal to the optical touch panel.

26. A method of driving a light sensing apparatus, the method comprising:
sequentially applying a negative first voltage, a negative second voltage
that is higher than the first voltage, and a positive third voltage to a
gate of an oxide semiconductor transistor that operates as both a light
sensing device sensing light and a switch outputting light sensing data.

27. The method of claim 26, wherein the first voltage is lower than a
first threshold voltage, and the second voltage is between the first
threshold voltage and a second threshold voltage, the first threshold
voltage being a threshold voltage of the oxide semiconductor transistor
when light is incident on the oxide semiconductor transistor, the second
threshold voltage being a threshold voltage of the oxide semiconductor
transistor when light not incident on the oxide semiconductor transistor.

28. The method of claim 27, wherein the third voltage is a reset signal
that resets the oxide semiconductor transistor.

29. The method of claim 27, further comprising: measuring current flowing
between a drain and a source of the oxide semiconductor transistor during
the application of the second voltage to a gate of the oxide
semiconductor transistor.

30. A method of driving a light sensing apparatus, the light sensing
apparatus comprising a plurality of light sensing pixels in a plurality
of rows and a plurality of columns, each of the light sensing pixels
including an oxide semiconductor transistor that operates as both a light
sensing device sensing light and a switch outputting light sensing data,
the method comprising: applying a negative second voltage to gates of the
oxide semiconductor transistors of the plurality of light sensing pixels
in a row from among the plurality of rows, and a negative first voltage
that is lower than the second voltage to the gates of the oxide
semiconductor transistors in other rows from among the plurality of rows;
sequentially applying the second voltage to the gates of the oxide
semiconductor transistors of the plurality of light sensing pixels in a
next row from among the plurality or rows, and applying the first voltage
to the gates of the oxide semiconductor transistors of the plurality of
light sensing pixels in rows other than the next row from among the
plurality of rows; and simultaneously applying a positive third voltage
to the gates of the oxide semiconductor transistors of the plurality of
the light sensing pixels in all the rows, after the sequential
application of the second voltage to all rows is completed.

31. The method of claim 30, wherein the first voltage is lower than a
first threshold voltage, and the second voltage is between the first
threshold voltage and a second threshold voltage, the first threshold
voltage being a threshold voltage of the oxide semiconductor transistor
when light is incident on the oxide semiconductor transistor, the second
threshold voltage being a threshold voltage of the oxide semiconductor
transistor when light not incident on the oxide semiconductor transistor.

32. The method of claim 31, wherein the third voltage is a reset signal
that resets the oxide semiconductor transistor.

33. The method of claim 31, further comprising: measuring current flowing
between a drain and a source of the oxide semiconductor transistor during
the application of the second voltage to a gate of the oxide
semiconductor transistor.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part application of U.S.
patent application Ser. No. 12/926,922, filed on Dec. 17, 2010, and
claims priority under 35 U.S.C. §119 to Korean Patent Application
No. 10-2010-0037531, filed on Apr. 22, 2010 in the Korean Intellectual
Property Office (KIPO) and Korean Patent Application No. 10-2011-0073779,
filed on Jul. 25, 2011 in the KIPO, the entire contents of which are
incorporated herein by reference.

BACKGROUND

[0002] 1. Field

[0003] The present disclosure relates to a light sensing circuit having a
simplified structure using an oxide semiconductor transistor capable of
sensing light as a light sensing device, a light sensing apparatus
including the light sensing circuit, a method of driving the light
sensing apparatus, and an image acquisition apparatus and optical touch
screen apparatus including the light sensing apparatus.

[0004] 2. Description of the Related Art

[0005] Touch screen devices are devices which may directly receive input
data through a screen by recognizing a position of, for example, a
finger, a stylus, or the like, touching the screen and performing a
particular process by a software routine. To this end, a touch screen
device may be equipped with a touch panel to perform the above function.
Such touch panels may include resistive overlay type touch panels,
capacitive overlay type touch panels, surface acoustic wave (SAW) type
touch panels, infrared beam type touch panels, piezoelectric type touch
panels, or the like. The touch screen device is widely used in a variety
of fields as an input device replacing a keyboard or a mouse.

[0006] A touch screen device that has been widely used employs a method of
directly touching a screen of a display device using a finger or a
stylus. However, as the size of a display device increases, the distance
between the display device and a user may increase. In this case, use of
the direct touch method may be difficult to adopt. Accordingly, optical
touch screen devices have been proposed that may perform the same
function as the existing touch screen by sensing light instead of sensing
contact of a finger or a stylus. An optical touch screen device may
facilitate communications not only between a user and a terminal but also
between a user and a user.

[0007] In order to realize such an optical touch panel, a relatively small
sized light sensing device for sensing light may be required. An
amorphous silicon thin film transistor (a-Si TFT) is one of generally
used light sensing devices. However, an a-Si TFT may not exhibit a
sufficient current change according to light. Accordingly, when light is
incident, electric charges generated in a photodiode are accumulated in a
capacitor for a predetermined period of time and then a signal related to
light intensity may be generated from the quantity of electric charges
accumulated in the capacitor. When a capacitor is used as above, a
sensing time may be delayed as long as the time for accumulating electric
charges in a capacitor. Also, as the size of an optical touch screen
device increases, parasitic capacitance may increase as well.

SUMMARY

[0008] Provided is a light sensing circuit using an oxide semiconductor
transistor as a light sensing device, a light sensing apparatus including
the light sensing circuit, a method of driving the light sensing
apparatus, and an image acquisition apparatus and optical touch screen
apparatus including the light sensing apparatus.

[0009] Additional aspects will be set forth in part in the description
which follows and, in part, will be apparent from the description, or may
be learned by practice of example embodiments.

[0010] According to example embodiments, a light sensing circuit may
include an oxide semiconductor transistor including a channel layer
including an oxide semiconductor material. The oxide semiconductor
transistor may be configured to operate as a light sensing device that
senses light and a switch that outputs light sensing data.

[0011] The light sensing circuit may further include a gate line connected
to a gate of the oxide semiconductor transistor and configured to provide
a gate voltage, a drive voltage line connected to a drain of the oxide
semiconductor transistor and configured to provide a drive voltage, and a
data line connected to a source of the oxide semiconductor transistor and
configured to provide data.

[0012] The light sensing circuit may further include a gate driver
configured to provide the gate voltage to the gate of the oxide
semiconductor transistor via the gate line. The gate driver may be
configured such that the gate voltage is any one of a first voltage that
is lower than a first threshold voltage, a second voltage that is between
the first threshold voltage and a second threshold voltage, and a third
voltage that is positive, the first threshold voltage being a threshold
voltage of the oxide semiconductor transistor when light is incident on
the oxide semiconductor transistor, the second threshold voltage being a
threshold voltage of the oxide semiconductor transistor when light not
incident on the oxide semiconductor transistor.

[0013] The light sensing circuit may further include a gate line connected
to both of a gate and a drain of the oxide semiconductor transistor and
configured to provide a gate voltage; and a data line connected to a
source of the oxide semiconductor transistor and configured to provide
data.

[0014] The oxide semiconductor transistor may include a substrate, a gate
disposed on at least a portion of the substrate, a gate insulation film
on the substrate and the gate to cover at least the gate, a channel layer
disposed on the gate insulation film to face the gate, a source and a
drain disposed to cover opposite sides of the channel layer, and a
transparent insulation layer disposed to cover the source, the drain, and
the channel layer, wherein the channel layer is formed on the gate
insulation film and facing the gate.

[0015] The oxide semiconductor transistor may further include a first
conductive plug that passes through the transparent insulation layer and
is electrically connected to the source; a first contact on the
transparent insulation that electrically contacts the first conductive
plug; a second conductive plug that passes through the transparent
insulation layer and is electrically connected to the drain; and a second
contact on the transparent insulation layer that electrically contacts
the second conductive plug.

[0016] The oxide semiconductor transistor may include a substrate; a gate
insulation film on at least a central portion of the channel layer; a
gate on the gate insulation film that faces the channel layer; a source
and a drain on the channel layer at opposite sides of the gate, the
source and drain each being separate from the gate; and a transparent
insulation layer covering the gate, the source, and the drain, the
channel layer being on the substrate.

[0017] The oxide semiconductor material may include one or more of ZnO,
InO, SnO, InZnO, ZnSnO, or InSnO, or a material formed by adding at least
one of Hf, Zr, Ti, Ta, Ga, Nb, V, Al, and Sn to one of ZnO, InO, SnO,
InZnO, ZnSnO, or InSnO.

[0018] According to another aspect of the present invention, a light
sensing apparatus may include a light sensing pixel array including a
plurality of light sensing pixels arranged in a plurality of rows and a
plurality of columns, and a gate driver including a plurality of gate
lines arranged in a row direction, the gate driver being configured to
provide a gate voltage and a reset signal to each of the plurality of
light sensing pixels via the plurality of gate lines, wherein each of the
plurality of light sensing pixels may include an oxide semiconductor
transistor configured to operate as both a light sensing device that
senses light and a switch that outputs light sensing data.

[0019] The gate driver may be configured to apply the gate voltage to the
oxide semiconductor transistors sequentially in the row direction, and to
apply the reset signal to all of the oxide semiconductor transistors at a
time after applying the gate voltage to the oxide semiconductor
transistors sequentially in the row direction.

[0020] The gate driver may provide each oxide semiconductor transistor
with a first voltage that is lower than a first threshold voltage, a
second voltage that is between the first threshold voltage and a second
threshold voltage, and a third voltage that is positive, the first
threshold voltage being a threshold voltage of the oxide semiconductor
transistor when light is incident on the oxide semiconductor transistor,
the second threshold voltage being a threshold voltage of the oxide
semiconductor transistor when light not incident on the oxide
semiconductor transistor.

[0021] The gate driver may be configured to provide the gate voltage to
each oxide semiconductor transistor in order of the first voltage, the
second voltage, the first voltage, and the third voltage, and the third
voltage is the reset signal to reset the oxide semiconductor transistor.

[0022] Each gate line may be connected light sensing pixels, from among
the plurality of light sensing pixels that are in the same row.

[0023] Gates of the oxide semiconductor transistors of the plurality of
light sensing pixels in a row may be connected to the gate line of the
same row.

[0024] The light sensing apparatus may further include a signal output
unit that includes a plurality of data lines arranged in a column
direction, the signal output unit being configured to receive a light
sensing signal from each of the plurality of light sensing pixel and
output a data signal.

[0025] Sources of the oxide semiconductor transistors of the plurality of
light sensing pixels in a column may be connected to the data line of the
same column.

[0026] The signal output unit may include an A/D converter configured to
convert analog signals output from the plurality of light sensing pixels
into digital signals, a buffer configured to temporarily store the
digital signals, and a column scanner configured to select an output from
one of the plurality of light sensing pixels in a column.

[0027] According to another aspect of the present invention, an image
acquisition apparatus includes the above light sensing circuit in a
pixel.

[0028] According to another aspect of the present invention, an image
acquisition apparatus include the above light sensing apparatus.

[0029] According to another aspect of the present invention, an optical
touch screen apparatus includes a display apparatus configured to display
an image, an optical touch panel attached on a screen of the display
apparatus and including the above light sensing circuit in a pixel, and a
light source apparatus configured to provide an optical signal to the
optical touch panel.

[0030] According to another aspect of the present invention, an optical
touch screen apparatus includes a display apparatus configured to display
an image, an optical touch panel attached on a screen of the display
apparatus and including the above light sensing apparatus, and a light
source apparatus configured to provide an optical signal to the optical
touch panel.

[0031] According to another aspect of the present invention, a method of
driving a light sensing apparatus includes sequentially applying a
negative (-) first voltage, a negative (-) second voltage that is higher
than the first voltage, and a positive third voltage to a gate of an
oxide semiconductor transistor that operates as both a light sensing
device sensing light and a switch outputting light sensing data.

[0032] The first voltage may be lower than a first threshold voltage, and
the second voltage may be between the first threshold voltage and a
second threshold voltage, the first threshold voltage being a threshold
voltage of the oxide semiconductor transistor when light is incident on
the oxide semiconductor transistor, the second threshold voltage being a
threshold voltage of the oxide semiconductor transistor when light not
incident on the oxide semiconductor transistor.

[0033] The third voltage may be a reset signal that resets the oxide
semiconductor transistor.

[0034] The method may further include measuring current flowing between a
drain and a source of the oxide semiconductor transistor during the
application of the second voltage to a gate of the oxide semiconductor
transistor.

[0035] According to another aspect of the present invention, a method of
driving a light sensing apparatus includes the light sensing apparatus
including a plurality of light sensing pixels being arranged in a
plurality of rows and a plurality of columns, each of the light sensing
pixels including an oxide semiconductor transistor that operates as both
of a light sensing device sensing light and a switch outputting light
sensing data, the method including applying a negative (-) second voltage
to gates of the oxide semiconductor transistors of the plurality of light
sensing pixels arranged in a row, from among the plurality of rows, and a
negative (-) first voltage that is lower than the second voltage to the
gates of the oxide semiconductor transistors arranged in the other rows
from among the plurality of rows, sequentially applying the second
voltage to the gates of the oxide semiconductor transistors of the
plurality of light sensing pixels arranged in a next row from among the
plurality of rows, and the first voltage to the gates of the oxide
semiconductor transistors of the plurality of light sensing pixels
arranged in the rows other than the next row from among the plurality of
rows, and, simultaneously applying a positive third voltage to the gates
of the oxide semiconductor transistors of the plurality of the light
sensing pixels arranged in all the rows, after the sequential application
of the second voltage to all rows is completed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The above and other features and advantages of example embodiments
will become more apparent by describing in detail example embodiments
with reference to the attached drawings. The accompanying drawings are
intended to depict example embodiments and should not be interpreted to
limit the intended scope of the claims. The accompanying drawings are not
to be considered as drawn to scale unless explicitly noted.

[0037] FIG. 1 is a cross-sectional view schematically illustrating a
structure of an oxide semiconductor transistor used as a light sensing
device according to example embodiments;

[0038]FIG. 2 is a cross-sectional view schematically illustrating a
structure of an oxide semiconductor transistor used as a light sensing
device according to example embodiments;

[0039] FIGS. 3 and 4 are graphs showing operation characteristics of the
oxide semiconductor transistors of FIGS. 1 and 2;

[0040]FIG. 5 is a circuit diagram illustrating a structure of a light
sensing circuit according to example embodiments;

[0041]FIG. 6 schematically illustrates operation characteristics and a
driving method of an oxide semiconductor transistor in the light sensing
circuit of FIG. 5;

[0042]FIG. 7 is a block diagram schematically illustrating a structure of
a light sensing apparatus according to example embodiments including the
light sensing circuit of FIG. 5;

[0043]FIG. 8 schematically illustrates a structure of a light sensing
pixel array of the light sensing apparatus of FIG. 7;

[0044]FIG. 9 is a timing diagram showing a method of driving the light
sensing apparatus of FIG. 7;

[0045]FIG. 10 is a circuit diagram illustrating a structure of a light
sensing circuit according to example embodiments;

[0046]FIG. 11 schematically illustrates operation characteristics and a
driving method of an oxide semiconductor transistor in the light sensing
circuit of FIG. 10; and

[0047]FIG. 12 is a perspective view of an optical touch screen apparatus
according to example embodiments in which the light sensing apparatus of
FIG. 7 is used as a light touch panel.

DETAILED DESCRIPTION

[0048] Detailed example embodiments are disclosed herein. However,
specific structural and functional details disclosed herein are merely
representative for purposes of describing example embodiments. Example
embodiments may, however, be embodied in many alternate forms and should
not be construed as limited to only the embodiments set forth herein.

[0049] Accordingly, while example embodiments are capable of various
modifications and alternative forms, embodiments thereof are shown by way
of example in the drawings and will herein be described in detail. It
should be understood, however, that there is no intent to limit example
embodiments to the particular forms disclosed, but to the contrary,
example embodiments are to cover all modifications, equivalents, and
alternatives falling within the scope of example embodiments. Like
numbers refer to like elements throughout the description of the figures.

[0050] It will be understood that, although the terms first, second, etc.
may be used herein to describe various elements, these elements should
not be limited by these terms. These terms are only used to distinguish
one element from another. For example, a first element could be termed a
second element, and, similarly, a second element could be termed a first
element, without departing from the scope of example embodiments. As used
herein, the term "and/or" includes any and all combinations of one or
more of the associated listed items.

[0051] It will be understood that when an element is referred to as being
"connected" or "coupled" to another element, it may be directly connected
or coupled to the other element or intervening elements may be present.
In contrast, when an element is referred to as being "directly connected"
or "directly coupled" to another element, there are no intervening
elements present. Other words used to describe the relationship between
elements should be interpreted in a like fashion (e.g., "between" versus
"directly between", "adjacent" versus "directly adjacent", etc.).

[0052] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of example
embodiments. As used herein, the singular forms "a", "an" and "the" are
intended to include the plural forms as well, unless the context clearly
indicates otherwise. It will be further understood that the terms
"comprises", "comprising,", "includes" and/or "including", when used
herein, specify the presence of stated features, integers, steps,
operations, elements, and/or components, but do not preclude the presence
or addition of one or more other features, integers, steps, operations,
elements, components, and/or groups thereof.

[0053] It should also be noted that in some alternative implementations,
the functions/acts noted may occur out of the order noted in the figures.
For example, two figures shown in succession may in fact be executed
substantially concurrently or may sometimes be executed in the reverse
order, depending upon the functionality/acts involved.

[0054] An oxide semiconductor transistor is, for example, a transistor in
which an oxide semiconductor is used as a material for a channel. The
oxide semiconductor transistor may have a characteristic of being
sensitive to light according to a material for an oxide semiconductor
that is used as a channel layer. When an oxide semiconductor material
having such a characteristic is used as a channel layer, an oxide
semiconductor transistor may be characterized in that a threshold voltage
and a drain current change according to a wavelength or light quantity of
incident light. Accordingly, the oxide semiconductor transistor may be
used as a light sensing device.

[0055] FIG. 1 is a cross-sectional view schematically illustrating a
structure of an oxide semiconductor transistor 10 used as a light sensing
device according to example embodiments. Referring to FIG. 1, the oxide
semiconductor transistor 10 may include a substrate 11, an insulation
layer 12 disposed on the substrate 11, a gate 13 disposed, for example
partially, on the insulation layer 12, a gate insulation film 14 disposed
on the insulation layer 12 and the gate 13 to cover at least the gate 13,
a channel layer 15 disposed on the gate insulation film 14 to face the
gate 13, a source 16 and a drain 17 disposed to cover the opposite sides
of the channel layer 15, and a transparent insulation layer 18 disposed
to cover the source 16, the drain 17, and the channel layer 15. Also, the
oxide semiconductor transistor 10 may include a first conductive plug 21
electrically connected to the source 16 by passing through the
transparent insulation layer 18 for electrical connection to the source
16, a first contact 23 formed on the transparent insulation layer 18 to
electrically contact the first conductive plug 21, a second conductive
plug 22 electrically connected to the drain 17 by passing through the
transparent insulation layer 18 for electrical connection to the drain
17, and a second contact 24 formed on the transparent insulation layer 18
to electrically contact the second conductive plug 22.

[0056] The substrate 11 may use a general substrate material, for example,
glass, silicon, or the like. The insulation layer 12, the gate insulation
film 14, and the transparent insulation layer 18 may use a material such
as SiO2. When the substrate 11 is formed of an insulation material,
the insulation layer 12 on the substrate 11 may be omitted. Also, the
gate 13, the source 16, and the drain 17 may use a conductive metal or
conductive metal oxide. For example, the oxide semiconductor transistor
10 that is sensitive to light may be used for an optical touch panel that
is attached to a display panel, the gate 13, the source 16, and the drain
17 may be formed of a transparent conductive material such as indium tin
oxide (ITO). However, when the oxide semiconductor transistor 10 is not
transparent, materials for the substrate 11, the insulation layer 12, the
gate 13, the gate insulation film 14, the source 16, and the drain 17 may
not be transparent. According to example embodiments, only the
transparent insulation layer 18 in the upper portion may be transparent
in order to guide light toward the channel layer 15.

[0057] The channel layer 15 may be formed of an oxide semiconductor
material, as described above. The oxide semiconductor transistor 10 may
have a light sensitive characteristic according to an oxide semiconductor
material for the channel layer 15. For example, an oxide semiconductor
material such as ZnO, InO, SnO, InZnO, ZnSnO, and InSnO may be used as an
oxide semiconductor channel material, or a material formed by adding at
least one of Hf, Zr, Ti, Ta, Ga, Nb, V, Al, and Sn to the above-described
oxide semiconductor material may be used as the oxide semiconductor
channel material. When the above material is used for the channel layer
15, the oxide semiconductor transistor 10 of FIG. 1 may exhibit a
threshold voltage and a drain current that change according to the
wavelength or light quantity of incident light and may be used as a light
sensing device. The channel layer 15 may be formed of a single oxide
semiconductor layer or may have a multilayer structure.

[0058] FIG. 1 illustrates the oxide semiconductor transistor 10 having a
bottom- gate structure in which a gate is arranged under a channel.
However, according to example embodiments a light sensing device may
include an oxide semiconductor transistor having a top-gate structure.
For example, FIG. 2 is a cross-sectional view schematically illustrating
a structure of an oxide semiconductor transistor 30 having a top-gate
structure according to example embodiments.

[0059] Referring to FIG. 2, according to example embodiments, the oxide
semiconductor transistor 30 may include a substrate 31, a channel layer
32 disposed on the substrate 31, a gate insulation film 33 disposed, for
example partially, on a central area of the channel layer 32, a gate 34
disposed on the gate insulation film 33 to face the channel layer 32, a
source 35 and a drain 36 disposed on the channel layer 32 to be separated
from the opposite sides of the gate 34, and a transparent insulation
layer 37 disposed to cover the gate 34, the source 35, and the drain 36.
According to example embodiments, In the oxide semiconductor transistor
30 having a top-gate structure of FIG. 2, in order for light to be
incident upon the channel layer 32, the gate 34, the source 35, and the
drain 36 may be formed of a transparent conductive material such as ITO.
Also, the oxide semiconductor transistor 30 of FIG. 2 may further include
the first conductive plug 21, the first contact 23, the second conductive
plug 22, and the second contact 24.

[0060] FIGS. 3 and 4 are graphs showing operation characteristics of the
oxide semiconductor transistor 10 of FIG. 1 and the oxide semiconductor
transistor 30 of FIG. 2 according to example embodiments. First, FIG. 3
shows a characteristic of a drain current Ids with respect to a gate
voltage Vgs for either the oxide semiconductor transistor 10 illustrated
in FIG. 2 or the oxide semiconductor 30 illustrated in FIG. 2. The
characteristic is shown for drain-to-source voltages Vds of 0.1, 5.1 and
10.1.

[0061]FIG. 3 illustrates first and second threshold voltages Vth1 and
Vth2. FIG. 3 also illustrates first through third voltages V1, V2 and V3.
FIG. 3 illustrates a characteristic of a drain current vs. a gate voltage
(Ids-Vgs) of the oxide semiconductor transistor 10 or 30 when light is
not incident or an amount of incident light is at or below a reference
level (indicated by the label `dark` in FIG. 3), and when light is
incident or an amount of incident light is at or above a second reference
level (indicated by the label `light` in FIG. 3). Referring to FIG. 3,
when light is incident on the oxide semiconductor transistor 10 or 30, it
can be seen that a threshold voltage may generally move in a negative
direction, for example, based on an amount of the incident light. For
example, in the example illustrated in FIG. 3, when light is not incident
on the oxide semiconductor transistor or an amount of incident light is
at or below a first reference level 10 or 30, the threshold voltage of
the oxide semiconductor transistor 10 or 30 is equal to the second
threshold voltage Vth2 and is changed to the first threshold voltage Vth1
when light is incident, for example, based on the amount of incident
light. Thus, when a gate voltage equal to the second voltage V2 between
the first threshold voltage Vth1 and the second threshold voltage Vth2 is
applied to the oxide semiconductor transistor 10 or 30, in the `dark`
case, the oxide semiconductor transistor 10 or 30 is may be in an OFF
state and thus a relatively low drain current may flow and, in the
`light` case, the oxide semiconductor transistor 10 or 30 is may be in an
ON state and thus a relatively high drain current may flow. Further, when
a gate voltage equal to the first voltage V1 is applied to the oxide
semiconductor transistor 10 or 30, the oxide semiconductor transistor 10
or 30 is may always be in the OFF state regardless of the incidence of
light. Also, when a gate voltage equal to the third voltage V3 higher
than the first and second threshold voltages Vth1 and Vth2 is applied to
the oxide semiconductor transistor 10 or 30, the oxide semiconductor
transistor 10 or 30 is may always be in the ON state regardless of the
incidence of light.

[0062] Thus, in a state in which a gate voltage equal to the second
voltage V2 is applied to the oxide semiconductor transistor 10 or 30, the
incidence of light may be determined by measuring the drain current. In
particular, in the case of the oxide semiconductor transistor 10 or 30,
it can be seen that a current ratio (ION/IOFF) between the
drain current when light is incident and the drain current when light is
not incident, or below a reference level, may be about 5.2
(log10(10-7.2/ 10-12)) which may be large compared to
conventional silicon semiconductor photodiodes. When the oxide
semiconductor transistor 10 or 30 having such a characteristic is used as
a light sensing device, there may be a variety of advantages. For
example, since a light sensitivity of the oxide semiconductor transistor
10 or 30 is high, when the oxide semiconductor transistor 10 or 30 is
used as a light sensing device, a circuit structure of a light sensing
pixel may be much simplified.

[0063] For a general silicon photodiode, since a current ratio is
relatively low, electric charges generated from a photodiode when light
is applied may be accumulated in a capacitor for a predetermined time and
then a signal representing light intensity may be generated from the
quantity of the electric charges accumulated in the capacitor. Thus, a
separate data output and switching drive circuit may be needed to convert
the electric charges accumulated in the capacitor into a light intensity
signal and output. To this end, a photodiode, a capacitor, and at least
one thin film transistor may be arranged for each light sensing pixel.
Typically, 3 to 5 thin film transistors may be used for one light sensing
pixel to amplify and output a signal without noise.

[0064] However, since light sensitivity of the oxide semiconductor
transistor 10 of FIG. 1 or the oxide semiconductor transistor 30 of FIG.
2 may be comparatively higher or very high with respect to conventional
photodiodes, there may be no need to accumulate electric charges in a
capacitor for a predetermined time. Also, since the oxide semiconductor
transistor 10 or 30 may be capable of performing a switch function by
itself unlike a photodiode, a separate data output and switching drive
circuit may not be necessary. Accordingly, the size of a light sensing
apparatus using the switch function may be increased, a drive speed may
be improved, and consumption of power may be reduced.

[0065]FIG. 4 is a graph showing a change in the drain current according
to the passage of time after light is incident on the oxide semiconductor
transistor 10 or the oxide semiconductor transistor 30, in which a gate
voltage Vg of, for example, -5V, between the first and second threshold
voltages Vth1 and Vth2, is applied to the oxide semiconductor transistor
10 or 30. In the example illustrated in FIG. 4, light becomes incident on
the oxide semiconductor 10 from the 40 second point to approximately the
55 second point. In the example illustrated in FIG. 4, the drain current
increases when light is incident on the oxide semiconductor transistor 10
or 30. However, even when the incidence of light discontinues at about 55
seconds, the drain current hardly decreases and rather maintains a
similar state to a light incidence state. According to example
embodiments, the oxide semiconductor transistor 10 or 30 has a sort of a
memory function with respect to the incidence of light. This phenomenon
may be understood as one in which electric charges are trapped in or on a
boundary surface of the channel layer 15 of the oxide semiconductor
transistor 10 or the channel layer 32 of the oxide semiconductor
transistor 30. For example, when a negative gate voltage is applied with
light to the oxide semiconductor transistor 10 or 30, holes generated by
the light in the channel layer 15 or 32 are transferred to a boundary
surface between the gate insulation film 14 or 33 and the channel layer
15 or 32 and may be trapped therein. The trapped electric charges may not
be removed until a sufficiently large positive voltage is applied to the
gate 13 or 34. Thus, once the electric charges are trapped, the drain
current may not be lowered even after the incidence of light
discontinues. Such a phenomenon may disappear when the trapped electric
charges are removed by applying a sufficiently large gate voltage to the
oxide semiconductor transistor 10 or 30.

[0066]FIG. 5 is a circuit diagram illustrating a structure of a light
sensing circuit 50 according to example embodiments. Referring to FIG. 5,
the light sensing circuit 50 may include a single oxide semiconductor
transistor 10 or 30 having light sensitivity, a gate line GATE connected
to the gate 13 or 34 of the oxide semiconductor transistor 10 or 30, a
drive voltage line Vdd connected to the drain 17 or 36 of the oxide
semiconductor transistor 10 or 30, and a data line DATA connected to the
source 16 or 35 of the oxide semiconductor transistor 10 or 30. The light
sensing circuit 50 configured as above may be capable of performing a
light sensing operation and a switching operation with the single oxide
semiconductor transistor 10 or 30 only, as described below. FIG. 5
illustrates the light sensing circuit 50 having only one pixel for
convenience of explanation. However, as described below, a plurality of
light sensing circuits 50 for a plurality of pixels may be arranged along
a plurality of gate lines GATE and a plurality of data lines DATA.

[0067]FIG. 6 schematically illustrates operation characteristics and a
driving method of the oxide semiconductor transistor 10 or 30 in the
light sensing circuit 50 of FIG. 5. Referring to FIG. 6, in a ready
state, the first voltage V1 that is negative and lower than the first
threshold voltage Vth1 when light is incident is applied to the gate 13
or 34 of the oxide semiconductor transistor 10 or 30 through the gate
line GATE. Then, the oxide semiconductor transistor 10 or 30 is always in
an OFF state regardless of the incidence of light. As a result, current
does not flow from the drain 17 or 36 of the oxide semiconductor
transistor 10 or 30 to the source 16 or 35 thereof. Thus, in the interim,
current hardly flows to the data line DATA.

[0068] Next, during transition `1` illustrated in FIG. 6, for the output
of a light sensing signal, the second voltage V2 that is negative and
between the first threshold voltage Vth1, which is a threshold voltage
during the incidence of light based on an amount of incident light, and
the second threshold voltage Vth2, which is a threshold voltage during
the non-incidence of light or the incidence of light below a first
reference amount, is applied to the gate 13 or 34 of the oxide
semiconductor transistor 10 or 30 through the gate line GATE. The second
voltage V2 is higher than the first voltage V1. As illustrated in FIG. 6,
the oxide semiconductor transistor 10 or 30 is in an ON state when light
is incident and in an OFF state when light is not incident. Thus, when
light is incident on the oxide semiconductor transistor 10 or 30, current
flows from the drain 17 or 36 to the source 16 or 35. According to
example embodiments, current may flow from the drive voltage line Vdd of
the light sensing circuit 50 to the data line DATA. The amount of current
flowing in the data line DATA may be proportional to the quantity or
intensity of incident light. Thus, the existence of incident light and
the quantity/intensity of incident light may be identified and calculated
by measuring the current flowing toward the data line DATA during when
the second voltage V2 is applied to the gate 13 or 34 of the oxide
semiconductor transistor 10 or 30. In particular, in order to improve
light sensitivity, the second voltage V2 may be selected between the
first threshold voltage Vth1 and the second threshold voltage Vth2 to be
closer to the second threshold voltage Vth2. When the output of a light
sensing signal is completed, during transition `2` illustrated in FIG. 6,
the first voltage V1 is applied again to the gate 13 or 34 of the oxide
semiconductor transistor 10 or 30 via the gate line GATE. Then, the oxide
semiconductor transistor 10 or 30 is in an OFF state regardless of the
existence of incident light.

[0069] As described above with reference to FIG. 4, once light is
incident, the drain current in the oxide semiconductor transistor 10 or
30 is not lowered even when the incidence of light discontinues.
Accordingly, after the output of a light sensing signal, for a next light
sensing operation, an operation to reset the oxide semiconductor
transistor 10 or 30 is performed by applying a sufficiently large amount
of a gate voltage to the oxide semiconductor transistor 10 or 30. For
example, referring to FIG. 6, during transition `3` illustrated in FIG.
6, a sufficiently large amount of the third voltage V3 is applied to the
gate 13 or 34 of the oxide semiconductor transistor 10 or 30 via the gate
line GATE. Then, the oxide semiconductor transistor 10 or 30 is reset and
thus the next light sensing operation may be performed. Thereafter,
during transition `4` illustrated in FIG. 6,the oxide semiconductor
transistor 10 or 30 is in a ready state while the first voltage V1 is
applied again to the gate 13 or 34 of the oxide semiconductor transistor
10 or 30 until the next light sensing operation is performed.

[0070] When the second voltage V2 is applied sequentially to the gate
lines GATE using the above principle, the pixel or pixels upon which
light is incident among a plurality of pixels may be indentified. As
described above, in the light sensing circuit 50 according to example
embodiments, one oxide semiconductor transistor 10 or 30 may perform both
of light sensing and data output. According to example embodiments, the
oxide semiconductor transistor 10 or 30 may simultaneously function as a
light sensing device and a drive circuit. Thus, it is possible to provide
the light sensing circuit 50 having a structure that is very simplified
as illustrated in FIG. 5.

[0071] The light sensing circuit 50 may be used for each pixel structure
of a light sensing apparatus such as a light touch screen apparatus or an
image acquisition apparatus. FIG. 7 is a block diagram schematically
illustrating a structure of a light sensing apparatus 100 according to
example embodiments including the light sensing circuit 50 of FIG. 5.
Referring to FIG. 7, the light sensing apparatus 100 according to example
embodiments may include a light sensing pixel array 120 having a
plurality of light sensing pixels 121 for sensing incident light, a gate
driver 110 that selectively supplies a gate voltage and a reset signal to
each of the light sensing pixels 121, and a signal output unit 130 that
receives a light sensing signal from each of the light sensing pixels 121
and outputs a data signal. As illustrated in FIG. 7, the light sensing
pixels 121 of the light sensing pixel array 120 may be arranged in a
plurality of rows and a plurality of columns. For example, the light
sensing pixels 121 may be arranged in an array of n-numbered rows and
m-numbered columns. Each of the light sensing pixels 121 may be formed of
a single oxide semiconductor transistor 10 or 30, as illustrated in FIG.
5. Also, the signal output unit 130 may include an analog-to-digital
(A/D) converter 131 for converting an analog output signal of the light
sensing pixels 121 into a digital signal, a data buffer 132 for
temporarily storing the digital output signal, and a column scanner 133
for selecting an output from the light sensing pixels 121 of a particular
column.

[0072]FIG. 8 schematically illustrates a structure of the light sensing
pixel array 120 of the light sensing apparatus 100 of FIG. 7. For
example, referring to FIG. 8, the light sensing circuit 50 of FIG. 5 is
illustrated as being arranged in each of the light sensing pixels 121.
However, instead of the light sensing circuit 50 of FIG. 5, a light
sensing circuit 60 of FIG. 10 may be arranged in each of the light
sensing pixels 121.

[0073] Referring to FIGS. 7 and 8, the gate driver 110 may selectively
activate each of the light sensing pixels 121 to control each of the
light sensing pixels 121 to output a light sensing signal. To this end,
the gate driver 110 may include a plurality of gate lines GATE1, GATE2, .
. . , which are arranged in a row direction. Each gate line may be
connected to the gates 13 or 34 of the oxide semiconductor transistor 10
or 30 in all of the light sensing pixels 121 arranged in the same row.
For example, the first gate line GATE1 may be connected to the gates 13
or 34 of the oxide semiconductor transistor 10 or 30 in all of the light
sensing pixels 121 arranged in the first row, and the second gate line
GATE2 may be connected to the gates 13 or 34 of the oxide semiconductor
transistor 10 or 30 in all of the light sensing pixels 121 arranged in
the second row.

[0074] The signal output unit 130 may receive a light sensing signal
generated from each of the light sensing pixels 121 and output a data
signal. To this end, the signal output unit 130 may include a plurality
of data lines Data1, Data2, . . . , which are arranged in a column
direction. Each of the data lines Data1, Data2, . . . , may be connected
to the source 16 or 35 of the oxide semiconductor transistor 10 or 30 in
all of the light sensing pixels 121 arranged in the same column. For
example, the first data line Data1 may be connected to the source 16 or
35 of the oxide semiconductor transistor 10 or 30 in all of the light
sensing pixels 121 arranged in the first column, and the second data line
Data2 may be connected to the source 16 or 35 of the oxide semiconductor
transistor 10 or 30 in all of the light sensing pixels 121 arranged in
the second column.

[0075] In the above-described structure, the signal output unit 130 may
simultaneously receive all light sensing signal generated from the light
sensing pixels 121 arranged in the same row through the data lines Data1,
Data2, . . . . For example, when a gate voltage V2 is applied to the
first gate line GATE1, all light sensing signals generated from the light
sensing pixels 121 arranged in the first row may be simultaneously input
to the signal output unit 130.

[0076] The signal output unit 130 may be configured to convert the light
sensing signals into digital data signals and sequentially output the
digital data signals column by column. For example, the output of each of
the light sensing pixels 121 is provided to the A/D converter 131 via the
corresponding data line DATA which may be connected top the signal output
unit 130. A signal from each of the light sensing pixels 121 may have a
high amplitude during the incidence of light and low amplitude, for
example, close to 0, during the non-incidence of light. Since the signal
at this time is an analog signal, the signal is converted into a digital
signal by the A/D converter 131. The digital output converted by the A/D
converter 131 may be provided to the data butter 132 and stored therein.
Then, the column scanner 133 may select a particular column such that
only a digital signal of the selected column is output according to the
selection of the column scanner 133. For example, FIG. 7 illustrates that
a signal of the light sensing pixel 121 located at the third row and
fourth column may be selected and output from the buffer 132.

[0077] The following description discusses the operation of the
above-described light sensing apparatus 100 according to example
embodiments. FIG. 9 is a timing diagram showing a method of driving the
light sensing apparatus 100 of FIG. 7. Referring to a timing diagram of
FIG. 9, first, the gate driver 110 may apply a gate voltage equal to a
second voltage V2 between the first and second threshold voltages Vth1
and Vth2 of the oxide semiconductor transistor 10 or 30 to the first gate
line GATE1 so that a light sensing signal is output from the light
sensing pixels 121 in the first row. A low voltage equal to a first
voltage V1 may be applied to the other gate lines GATE2, . . . . Thus,
light sensing signals may not be generated from the light sensing pixels
121 in the other rows. Then, the gate driver 110 may apply a gate voltage
V2 to the second gate line GATE2 so that a light sensing signal is output
from the light sensing pixels 121 in the second row. A low voltage V1 may
be applied to the other gate lines GATE1, GATE3, . . . . Thus, light
sensing signals may be output from the light sensing pixels 121 in order
from the first row to the last row of the light sensing pixel array 120
in this manner.

[0078] Then, the gate driver 110 may apply a positive reset signal equal
to a third voltage V3 to all of the gate lines GATE1, GATE2, . . . to
reset the oxide semiconductor transistor 10 or 30 of all of the light
sensing pixels 121 in the light sensing pixel array 120. Accordingly, the
oxide semiconductor transistor 10 or 30 is initialized so that a next
light sensing operation may be performed. As a result, a light sensing
operation of one frame is completed. When a light sensing operation of
one frame is completed, a light sensing operation of a next frame may be
repeated in the same order as that described above.

[0079]FIG. 10 is a circuit diagram illustrating a structure of a light
sensing circuit 60 according to example embodiments. FIG. 11
schematically illustrates operation characteristics and a driving method
of an oxide semiconductor transistor in the light sensing circuit 60 of
FIG. 10 according to example embodiments. As it can be seen from the
characteristic graph in the example illustrated in FIG. 11, in the oxide
semiconductor transistor 10 or 30 used in the light sensing circuit 60 of
FIG. 10, the first threshold voltage Vth1 during the incidence of light
is a negative voltage and the second threshold voltage Vth2 during the
non-incidence of light, or the incidence of light below a reference
amount, is a positive voltage. Such a threshold voltage characteristic
may be selected according to, for example, the material for the channel
layer 15 or 32. When the second threshold voltage Vth2 is a positive
voltage, the second voltage V2 provided to the gates 13 or 34 of the
oxide semiconductor transistor 10 or 30 via the gate line GATE may be a
positive voltage. In this case, without applying a separate drive voltage
Vdd to the drain 17 or 36 of the oxide semiconductor transistor 10 or 30,
the second voltage V2 applied to the gates 13 or 34 may be used as a
drive voltage. Thus, the light sensing circuit 60 of FIG. 10 may not
separately include a drive voltage Vdd line. The gate line GATE may be
simultaneously connected to the gates 13 or 34 and the drain 17 or 36 of
the oxide semiconductor transistor 10 or 30. The other structure and
operation of the light sensing circuit 60 of FIG. 10 may be the same as
those of the light sensing circuit 50 of FIG. 5.

[0080] As described above, each of the light sensing pixels 121 of the
light sensing apparatus 100 according to example embodiments may simply
include only one oxide semiconductor transistor 10 or 30. In the light
sensing apparatus 100, the oxide semiconductor transistor 10 or 30 may
function not only as a light sensor but also as a switch to output a
light sensing signal. Thus, compared to a conventional light sensing
apparatus which may have a more complicated circuit structure in which a
plurality of transistors and capacitors are installed in one pixel, the
structure and operation of the light sensing apparatus 100 according to
example embodiments may be much simplified. Accordingly, the light
sensing apparatus 100 may be manufactured in a large size overcoming a
design limit due to parasitic resistance and parasitic capacitance. Also,
an aperture ratio may be improved due to a simplified pixel structure so
that sensitivity and resolution of the light sensing apparatus 100 may be
improved.

[0081]FIG. 12 is a perspective view of an optical touch screen apparatus
200 according to example embodiments in which the light sensing apparatus
100 of FIG. 7 is used, for example, as a light touch panel. Referring to
FIG. 12, the optical touch screen apparatus 200 may include a display
apparatus 210 in which an optical touch panel formed of the
above-described light sensing apparatus 100 is attached to a screen. In
the optical touch screen apparatus 200, when light is irradiated to the
display apparatus 210 by using a light source apparatus 220 such as a
laser pointer, the light sensing pixels 121 arranged in the light sensing
apparatus 100 recognize the light. Thus, the same effect as one such as
touching a touch screen with a finger or a stylus may be obtained.

[0082] The above descriptions focus on the application, to the optical
touch screen apparatus 200, of the light sensing apparatus 100 including
the light sensing circuit 50 or 60 using the oxide semiconductor
transistor 10 or 30. However, the above-described light sensing apparatus
100 may be applied not only to the optical touch screen apparatus 200,
but also to other apparatuses including, for example, any or all
apparatuses for sensing light. For example, the above-described light
sensing apparatus 100 may be applied to an image acquisition apparatus
such as a CMOS image sensor or a CCD.

[0083] As described above, according to example embodiments, a light
sensing circuit having a simplified structure, a light sensing apparatus
including the light sensing circuit, a method of driving the light
sensing apparatus, and an image acquisition apparatus and optical touch
screen apparatus including the light sensing apparatus, are described and
illustrated. It should be understood example embodiments described
therein should be considered in a descriptive sense only and not for
purposes of limitation. Descriptions of features or aspects within
example embodiments should typically be considered as available for other
similar features or aspects in other example embodiments.

[0084] Example embodiments having thus been described, it will be obvious
that the same may be varied in many ways. Such variations are not to be
regarded as a departure from the intended spirit and scope of example
embodiments, and all such modifications as would be obvious to one
skilled in the art are intended to be included within the scope of the
following claims.